Rendering a 2d sprite is as simple (or not simple depending on how you look at it as rendering a quad with some texture coordinates. I'd suggest looking into getting the OpenGL Programming Guide (3rd ed), usually refered to as "the open red book". I find nehe's tutorials a really awful way to learn opengl.

Its also occured to me you might be asking about a technique called "billboarding." Billboarding is where a 2d sprite is rendered so its always facing the player. That topic is a little more involved, so I wont bother unless thats what you were asking about.

glOrtho is just a projection mode. z axis is specified (otherwise why specify near and far cliping planes with glOrtho?) but of course z translations are not visible for one single object. If you depth-test your objects, you'll see that far objects are occluded by near ones.

Besides using textured quads with glOrtho for sprites, and IFF it's only 2d images you want, there is also glDrawPixels, but it's too rigid to do anything fancy with it. Just puts a rectangular pixel area on screen...

If you depth-test your objects, you'll see that far objects are occluded by near ones.

Here is a compiled, and source code version of a OpenGL ortho mode project I was doing to see how fast I could get OpenGL on low end graphics cards, as well as learn OpenGL vertex arrays.

The demo also shows the far objects occluded by the card that zooms to and away from the screen as well you can see the mipmap (level of detail) effects on the cards as the zooming card goes back to its farthest point.